A limiting factor in the performance of an internal combustion engine is the amount of combustion air that can be delivered to the intake manifold for combustion in the engine cylinders. Atmospheric pressure is often inadequate to supply the required amount of air for proper operation of an engine at high efficiency. Therefore, it is common practice to use an auxiliary system to supply additional air to the intake manifold.
An internal combustion engine may include one or more turbochargers for compressing air that is then supplied to the combustion cylinders. Each turbocharger typically includes a turbine driven by exhaust gases of the engine, and a compressor that is driven by the turbine. The compressor receives air to be compressed, and supplies the compressed air to the combustion cylinder. The turbocharger supplies combustion air to the engine at a higher pressure and higher density than atmospheric pressure and ambient density. The turbocharger can be used to make up for a loss of power due to altitude, or to increase the power that can be obtained from an engine of a given displacement, thereby reducing the cost, weight and size of an engine for a given power output.
Many on the highway truck diesel engines use a divided exhaust manifold system. A divided exhaust system helps preserve the exhaust pulse energy from the cylinders, to be provided to the turbocharger for more efficient operation. At the instant that exhaust valve opens at the start of an exhaust cycle for a combustion cylinder, the cylinder is filled with hot gas at a high temperature. When the valve opens, exhaust gas immediately surges from the cylinder and travels past the exhaust valve or port at high velocity. A major portion of the exhaust gas surges from the cylinder during this short period. During the remainder of the exhaust cycle, while the exhaust valve remains open, a remaining portion of the exhaust gas continues to escape from the cylinder, due either to the upward travel of the piston or to the flow of air entering the cylinder. Thus, in looking at an entire exhaust gas cycle, as the exhaust valve opens an initial surge of exhaust gas occurs, which contains substantial portion of the overall energy available. This surge is typically followed by a much longer period with gas flow at much lower velocity. Preserving the energy in the exhaust pulses, to be conveyed to the turbine, improves overall turbocharger performance efficiency.
It is also common to use exhaust gas recirculation systems (EGR systems) for controlling the generation of undesirable pollutant gases and particulate matter in the operation of an internal combustion engine. EGR systems have proven particularly useful for on the road motor equipment. In a typical EGR system, exhaust gas byproducts are recirculated to the intake air supply of the internal combustion engine. The result is a decrease in the concentration of oxygen, which in turn lowers the maximum combustion temperature within the cylinder, and slows the chemical reaction of the combustion process, thereby decreasing the formation of nitrous oxides (NOX). Unburned hydrocarbons in the exhaust gases can be burned on reintroduction to the engine cylinder, further reducing the emission of exhaust gas byproducts.
When utilizing EGR in a turbocharged diesel engine, the exhaust gas to be recirculated is normally removed upstream of the exhaust gas driven turbine associated with the turbocharger. In many applications, the exhaust gas is diverted directly from the exhaust manifold. In a divided exhaust manifold system, an EGR system is typically designed to take exhaust gas from both sides of the divided nanifold system. Using this approach, it is difficult to preserve the exhaust pulse energy from the cylinders to the turbocharger.
EGR systems removing exhaust gases from both sides of a divided manifold greatly diminish the pulse energy available from the system.
Divided turbine housings are known. For example, U.S. Pat. No. 3,614,259 entitled, "Turbine Casing", discloses a turbine having a divided volute in the housing, with a flapper valve controlling the flow to each of the volute portions. Divided exhaust manifolds directed to separate turbine inlets are know, for example, from U.S. Pat. No. 3,383,092 entitled "Gas Turbine With Pulsating Gas Flows". Neither compensates for reduced exhaust flow from an exhaust manifold supplying EGR flow.
The present invention is directed to overcoming one or more of the problems as set forth above.